Whole Body Manipulation on a Legged Robot Using Dynamic Balance

ABSTRACT

A robot system includes: an upper body section including one or more end-effectors; a lower body section including one or more legs; and an intermediate body section coupling the upper and lower body sections. An upper body control system operates at least one of the end-effectors. The intermediate body section experiences a first intermediate body linear force and/or moment based on an end-effector force acting on the at least one end-effector. A lower body control system operates the one or more legs. The one or more legs experience respective surface reaction forces. The intermediate body section experiences a second intermediate body linear force and/or moment based on the surface reaction forces. The lower body control system operates the one or more legs so that the second intermediate body linear force balances the first intermediate linear force and the second intermediate body moment balances the first intermediate body moment.

CROSS REFERENCE TO RELATED APPLICATIONS

This U.S. patent application is a continuation of, and claims priorityunder 35 U.S.C. § 120 from, U.S. patent application Ser. No. 15/377,599,filed on Dec. 13, 2016. The disclosure of this prior application isconsidered part of the disclosure of this application and is herebyincorporated by reference in its entirety.

BACKGROUND

A robot may include a plurality of legs that are operable to balance therobot on a ground surface or to move the robot along the ground surface.The robot may also include one or more end-effectors that allow therobot to manipulate objects or support loads.

SUMMARY

According to example implementations, a robot can operate its legs todynamically balance itself on a surface while operating itsend-effectors. When the legs contact a surface (e.g., ground surface),the legs apply forces to the surface and experience reaction forces fromthe surface. The robot can dynamically control the legs so that thereaction forces allow the robot to maintain a balance that supports theoperation of the end-effectors. The dynamic balancing provided by thelegs during operation of the end-effectors constitutes a whole bodymanipulation that more closely resembles actual motion by actual humans.

According to an example implementation, a robot system includes a body.The body includes: an upper body section including one or more movableend-effectors; a lower body section including one or more legsconfigured to contact a surface; and an intermediate body sectioncoupling the upper body section and the lower body section.

The robot system also includes a control system implemented with one ormore processors. The control system includes an upper body controlsystem configured to operate at least one of the end-effectors. The atleast one end-effector experiences an end-effector force based on theoperation by the upper body control system. The intermediate bodysection experiences at least one of a first intermediate body linearforce or a first intermediate body moment based on the end-effectorforce. The control system includes a lower body control systemconfigured to operate the one or more legs in response to the operationof the at least one end-effector. The one or more legs experiencesrespective reaction forces from the surface based on the operation bythe lower body control system. The intermediate body section experiencesat least one of a second intermediate body linear force or a secondintermediate body moment based on the reaction forces. The lower bodycontrol system operates the one or more legs so that the secondintermediate body linear force balances the first intermediate linearforce and the second intermediate body moment balances the firstintermediate body moment.

According to another example implementation, a robot system includes abody. The body includes: an upper body section including one or moremovable end-effectors; a lower body section including one or more legsconfigured to contact a surface; and an intermediate body sectioncoupling the upper body section and the lower body section. The robotsystem includes a control system implemented with one or moreprocessors. The control system includes a lower body control system andan upper control system. A method for controlling a robot systemincludes operating, with the upper body control system, at least one ofthe end-effectors. The at least one end-effector experiences anend-effector force based on the operation by the upper body controlsystem. The intermediate body section experiences at least one of afirst intermediate body linear force or a first intermediate body momentbased on the end-effector force. The method includes operating, with thelower body control system, the one or more legs in response to theoperation of the at least one end-effector. The one or more legsexperiences respective reaction forces from the surface based on theoperation by the lower body control system. The intermediate bodysection experiences at least one of a second intermediate body linearforce or a second intermediate body moment based on the reaction forces.

According to yet another example implementation, a robot system includesa body. The body includes: an upper body section including one or moremovable end-effectors; a lower body section including one or more legsconfigured to contact a surface; and an intermediate body sectioncoupling the upper body section and the lower body section. The robotsystem includes a control system implemented with one or moreprocessors. The control system includes an upper body control systemconfigured to operate at least one of the end-effectors. The at leastone end-effector experiences an end-effector force based on theoperation by the upper body control system. The intermediate bodysection experiences at least one of a first intermediate body linearforce or an first intermediate body moment based on the at least oneend-effector force. The control system includes a lower body controlsystem configured to operate the one or more legs based on the firstintermediate body linear force or the first intermediate body moment.The one or more legs experiences respective reaction forces from thesurface based on the operation by the lower body control system. Theintermediate body section experiences at least one of a secondintermediate body linear force or a second intermediate body momentbased on the reaction forces. The lower body control system operates theone or more legs so that the second intermediate body linear forcebalances the first intermediate linear force and the second intermediatebody moment balances the first intermediate body moment. The upper bodycontrol system processes the lower body section as a virtual linkcoupled to the intermediate body section. The lower body control systemis further configured to position the intermediate body sectionaccording to a first set of degrees of freedom based on the operation ofthe one or more legs. The upper body control system is furtherconfigured to position the intermediate body section according to asecond set of degrees of freedom based on the operation of the at leastone end-effector The upper body control system is constrained frompositioning the intermediate body section according to the first set ofdegrees of freedom.

According to a further example implementation, a robot system includes abody. The body includes: an upper body section; a lower body sectionincluding one or more legs configured to contact a surface; and anintermediate body section coupling the upper body section and the lowerbody section. The robot system includes a control system implementedwith one or more processors. The control system includes an upper bodycontrol system configured to operate the upper body section. The upperbody section experiences an upper body force in response to theoperation by the upper body control system. The intermediate bodysection experiences at least one of a first intermediate body linearforce or a first intermediate body moment based on the upper body force.The control system includes a lower body control system configured tooperate the one or more legs. The one or more legs experiencesrespective reaction forces from the surface based on the operation bythe lower body control system. The intermediate body section experiencesat least one of a second intermediate body linear force or a secondintermediate body moment based on the reaction forces. The lower bodycontrol system operates the one or more legs so that the secondintermediate body linear force balances the first intermediate linearforce and the second intermediate body moment balances the firstintermediate body moment.

These as well as other aspects, advantages, and alternatives will becomeapparent to those of ordinary skill in the art by reading the followingdetailed description with reference where appropriate to theaccompanying drawings. Further, it should be understood that thedescription provided in this summary section and elsewhere in thisdocument is intended to illustrate the claimed subject matter by way ofexample and not by way of limitation.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a configuration of a robotic system according to anexample implementation.

FIG. 2 illustrates a quadruped robot according to an exampleimplementation.

FIG. 3 illustrates a biped robot according to an example implementation.

FIG. 4A illustrates a biped robot where dynamic balance is employed forwhole body manipulation according to an example implementation.

FIG. 4B illustrates an example of dynamic balancing by the biped robotof FIG. 4A according to an example implementation.

FIG. 4C illustrates another example of dynamic balancing by the bipedrobot of FIG. 4A while the robot operates an end-effector according toan example implementation.

FIG. 4D illustrates an exploded view of the biped robot of FIG. 4A.

FIG. 5 illustrates a configuration of a robotic system where dynamicbalance is employed for whole body manipulation according to an exampleimplementation.

FIG. 6 illustrates a method for operating a robot where dynamic balanceis employed for whole body manipulation according to an exampleimplementation.

DETAILED DESCRIPTION

The following detailed description describes various features andfunctions of the disclosed systems and methods with reference to theaccompanying figures. The illustrative system and method embodimentsdescribed herein are not meant to be limiting. It will be readilyunderstood that certain aspects of the disclosed systems and methods canbe arranged and combined in a wide variety of different configurations,all of which are contemplated herein.

I. OVERVIEW

A robot may include a plurality of legs that are operable to balance therobot on a ground surface or to move the robot along the ground surface.The robot may also include one or more end-effectors that allow therobot to manipulate objects or support loads. According to one approach,the robot must first operate its legs to maintain position control andestablish static balance before it can position the end-effectors toperform a task. For instance, the robot may initially operate the legsto form a static support polygon over which the center of mass of therobot is maintained during the positioning and operation of theend-effectors. According to this approach, the legs and theend-effectors are not simultaneously manipulated to act as a whole body.

According to example implementations disclosed herein, however, a robotcan operate its legs to dynamically balance itself on a surface while itoperates end-effectors. When the legs contact a surface (e.g., groundsurface), the legs apply forces to the surface and experience reactionforces from the surface. The robot can dynamically control the legs sothat the reaction forces allow the robot to maintain a balance thatsupports the operation of the end-effectors. The dynamic balancingprovided by the legs during operation of the end-effectors constitutes awhole body manipulation that may more closely resemble actual motion byactual humans.

The legs can dynamically balance the robot even while the robot ismoving according to a gait. For instance, the robot can walk or runalong a ground surface, and due to dynamic balancing, the robot cansimultaneously position the end-effector to grab an object withoutinterrupting the gait.

In example implementations, the robot includes a lower body section, anupper body section, and an intermediate body section. For a bipedalrobot, the intermediate section may act as, or resemble, a pelvis. Thelower body section includes the legs and the upper body section includesthe end-effectors. In some cases, the end-effectors may be disposed onthe ends of arms that can extend outwardly from the robot to positionthe end-effectors. The lower body section is coupled to the intermediatesection from below, and the upper body section is coupled to theintermediate section from above.

The robot includes a lower body control system and an upper body controlsystem. The lower body control system controls the legs, and the upperbody control system controls the end-effectors. The lower body controlsystem and the upper body control system coordinate to achieve wholebody manipulation and balance for the robot. In particular, the lowerbody control system controls the legs so that the reaction forces fromthe surface provide a dynamic balance that allows the upper body controlsystem to perform tasks with the end-effectors.

During its analysis, the upper body control system represents andprocesses the lower body section as a virtual link coupled to theintermediate body section. To position and operate the end-effectors,the upper body control system employs an inverse kinematics solver thataccounts for the virtual link as well as the position and orientation ofthe intermediate body section. Inverse kinematics refers to the use ofthe kinematics equations of the robot to determine the parameters forcomponents (e.g., joints) to allow an end-effector to reach a targetposition and perform a task. A motion plan specifies the movement of therobot so that the end-effector can reach a target position and perform atask. For instance, the inverse kinematics solver may use the velocityof the virtual link to determine a motion plan for the upper bodysection that achieves desired end-effector velocities in a static worldframe. Inverse kinematics transforms the motion plan into actuatortrajectories for components (e.g., joints) of the robot.

To position the end-effectors, the upper body control system mayreposition/reorient the intermediate body section. In general, theintermediate body section can be positioned and oriented according toany one or more of six degrees of freedom. To achieve dynamic balance,however, the lower body control system may need to reposition/reorientthe intermediate body section according to one or more of these sixdegrees of freedom. As such, to maintain the dynamic balance, the upperbody control system may be constrained from repositioning/reorientingthe intermediate body section according to the degrees of freedom neededby the lower body control system to achieve the dynamic balance. Inother words, the inverse kinematics solver for the upper body controlsystem treats these particular degrees of freedom as constraints. Theseconstraints free the lower body control system to balance dynamically.

The loads supported by the end-effectors generate a resulting linearforce and/or moment on the intermediate body section. The upper bodycontrol system can determine the resulting linear force and moment andcommunicate this information to the lower body control system. Inresponse, the lower body control system can operate the legs so that thereaction forces can balance the linear force and/or moment at theintermediate body section. In general, a first force/moment is balancedby a second force/moment, when the second force/moment directionallyopposes the first force/moment with at least substantially the samemagnitude.

Such balancing can also be employed when other loads are additionally oralternatively experienced by the upper body section. For instance, upperbody section may experience dynamic forces, such as forces required toaccelerate an arm, an end-effector, or a payload, during high-speedmotions. Such dynamic forces also generate a resulting linear forceand/or moment on the intermediate body section, which the lower bodycontrol can also balance with the reaction forces.

Additionally, when the upper body control system wants to extend theend-effectors to a target position, the lower body control system candetermine whether the current position of the legs allows theend-effectors to reach the target position with sufficient balance. Ifnecessary, the legs can be operated to move the robot along the surfaceso that the end-effectors can reach the target position.

II. EXAMPLE ROBOTIC SYSTEMS

FIG. 1 illustrates an example configuration of a robotic system that maybe used in connection with the implementations described herein. Therobotic system 100 may be configured to operate autonomously,semi-autonomously, and/or using directions provided by user(s). Therobotic system 100 may be implemented in various forms, such as a bipedrobot, quadruped robot, or some other arrangement. Furthermore, therobotic system 100 may also be referred to as a robot, robotic device,or mobile robot, among other designations.

As shown in FIG. 1, the robotic system 100 may include processor(s) 102,data storage 104, and controller(s) 108, which together may be part of acontrol system 118. The robotic system 100 may also include sensor(s)112, power source(s) 114, mechanical components 110, and electricalcomponents 116. Nonetheless, the robotic system 100 is shown forillustrative purposes, and may include more or fewer components. Thevarious components of robotic system 100 may be connected in any manner,including wired or wireless connections. Further, in some examples,components of the robotic system 100 may be distributed among multiplephysical entities rather than a single physical entity. Other exampleillustrations of robotic system 100 may exist as well.

Processor(s) 102 may operate as one or more general-purpose hardwareprocessors or special purpose hardware processors (e.g., digital signalprocessors, application specific integrated circuits, etc.). Theprocessor(s) 102 may be configured to execute computer-readable programinstructions 106, and manipulate data 107, both of which are stored inthe data storage 104. The processor(s) 102 may also directly orindirectly interact with other components of the robotic system 100,such as sensor(s) 112, power source(s) 114, mechanical components 110,and/or electrical components 116.

The data storage 104 may be one or more types of hardware memory. Forexample, the data storage 104 may include or take the form of one ormore computer-readable storage media that can be read or accessed byprocessor(s) 102. The one or more computer-readable storage media caninclude volatile and/or non-volatile storage components, such asoptical, magnetic, organic, or another type of memory or storage, whichcan be integrated in whole or in part with processor(s) 102. In someimplementations, the data storage 104 can be a single physical device.In other implementations, the data storage 104 can be implemented usingtwo or more physical devices, which may communicate with one another viawired or wireless communication. As noted previously, the data storage104 may include the computer-readable program instructions 106 and thedata 107. The data 107 may be any type of data, such as configurationdata, sensor data, and/or diagnostic data, among other possibilities.

The controller 108 may include one or more electrical circuits, units ofdigital logic, computer chips, and/or microprocessors that areconfigured to (perhaps among other tasks), interface between anycombination of the mechanical components 110, the sensor(s) 112, thepower source(s) 114, the electrical components 116, the control system118, and/or a user of the robotic system 100. In some implementations,the controller 108 may be a purpose-built embedded device for performingspecific operations with one or more subsystems of the robotic device100.

The control system 118 may monitor and physically change the operatingconditions of the robotic system 100. In doing so, the control system118 may serve as a link between portions of the robotic system 100, suchas between mechanical components 110 and/or electrical components 116.In some instances, the control system 118 may serve as an interfacebetween the robotic system 100 and another computing device. Further,the control system 118 may serve as an interface between the roboticsystem 100 and a user. The instance, the control system 118 may includevarious components for communicating with the robotic system 100,including a joystick, buttons, and/or ports, etc. The example interfacesand communications noted above may be implemented via a wired orwireless connection, or both. The control system 118 may perform otheroperations for the robotic system 100 as well.

During operation, the control system 118 may communicate with othersystems of the robotic system 100 via wired or wireless connections, andmay further be configured to communicate with one or more users of therobot. As one possible illustration, the control system 118 may receivean input (e.g., from a user or from another robot) indicating aninstruction to perform a particular gait in a particular direction, andat a particular speed. A gait is a pattern of movement of the limbs ofan animal, robot, or other mechanical structure.

Based on this input, the control system 118 may perform operations tocause the robotic device 100 to move according to the requested gait. Asanother illustration, a control system may receive an input indicatingan instruction to move to a particular geographical location. Inresponse, the control system 118 (perhaps with the assistance of othercomponents or systems) may determine a direction, speed, and/or gaitbased on the environment through which the robotic system 100 is movingen route to the geographical location.

Operations of the control system 118 may be carried out by theprocessor(s) 102. Alternatively, these operations may be carried out bythe controller 108, or a combination of the processor(s) 102 and thecontroller 108. In some implementations, the control system 118 maypartially or wholly reside on a device other than the robotic system100, and therefore may at least in part control the robotic system 100remotely.

Mechanical components 110 represent hardware of the robotic system 100that may enable the robotic system 100 to perform physical operations.As a few examples, the robotic system 100 may include physical memberssuch as leg(s), arm(s), and/or wheel(s). The physical members or otherparts of robotic system 100 may further include actuators arranged tomove the physical members in relation to one another. The robotic system100 may also include one or more structured bodies for housing thecontrol system 118 and/or other components, and may further includeother types of mechanical components. The particular mechanicalcomponents 110 used in a given robot may vary based on the design of therobot, and may also be based on the operations and/or tasks the robotmay be configured to perform.

In some examples, the mechanical components 110 may include one or moreremovable components. The robotic system 100 may be configured to addand/or remove such removable components, which may involve assistancefrom a user and/or another robot. For example, the robotic system 100may be configured with removable arms, hands, feet, and/or legs, so thatthese appendages can be replaced or changed as needed or desired. Insome implementations, the robotic system 100 may include one or moreremovable and/or replaceable battery units or sensors. Other types ofremovable components may be included within some implementations.

The robotic system 100 may include sensor(s) 112 arranged to senseaspects of the robotic system 100. The sensor(s) 112 may include one ormore force sensors, torque sensors, velocity sensors, accelerationsensors, position sensors, proximity sensors, motion sensors, locationsensors, load sensors, temperature sensors, touch sensors, depthsensors, ultrasonic range sensors, infrared sensors, object sensors,and/or cameras, among other possibilities. Within some examples, therobotic system 100 may be configured to receive sensor data from sensorsthat are physically separated from the robot (e.g., sensors that arepositioned on other robots or located within the environment in whichthe robot is operating).

The sensor(s) 112 may provide sensor data to the processor(s) 102(perhaps by way of data 107) to allow for interaction of the roboticsystem 100 with its environment, as well as monitoring of the operationof the robotic system 100. The sensor data may be used in evaluation ofvarious factors for activation, movement, and deactivation of mechanicalcomponents 110 and electrical components 116 by control system 118. Forexample, the sensor(s) 112 may capture data corresponding to the terrainof the environment or location of nearby objects, which may assist withenvironment recognition and navigation. In an example configuration,sensor(s) 112 may include RADAR (e.g., for long-range object detection,distance determination, and/or speed determination), LIDAR (e.g., forshort-range object detection, distance determination, and/or speeddetermination), SONAR (e.g., for underwater object detection, distancedetermination, and/or speed determination), VICON® (e.g., for motioncapture), one or more cameras (e.g., stereoscopic cameras for 3Dvision), a global positioning system (GPS) transceiver, and/or othersensors for capturing information of the environment in which therobotic system 100 is operating. The sensor(s) 112 may monitor theenvironment in real time, and detect obstacles, elements of the terrain,weather conditions, temperature, and/or other aspects of theenvironment.

Further, the robotic system 100 may include sensor(s) 112 configured toreceive information indicative of the state of the robotic system 100,including sensor(s) 112 that may monitor the state of the variouscomponents of the robotic system 100. The sensor(s) 112 may measureactivity of systems of the robotic system 100 and receive informationbased on the operation of the various features of the robotic system100, such the operation of extendable legs, arms, or other mechanicaland/or electrical features of the robotic system 100. The data providedby the sensor(s) 112 may enable the control system 118 to determineerrors in operation as well as monitor overall operation of componentsof the robotic system 100.

As an example, the robotic system 100 may use force sensors to measureload on various components of the robotic system 100. In someimplementations, the robotic system 100 may include one or more forcesensors on an arm or a leg to measure the load on the actuators thatmove one or more members of the arm or leg. As another example, therobotic system 100 may use one or more position sensors to sense theposition of the actuators of the robotic system. For instance, suchposition sensors may sense states of extension, retraction, or rotationof the actuators on arms or legs.

As another example, the sensor(s) 112 may include one or more velocityand/or acceleration sensors. For instance, the sensor(s) 112 may includean inertial measurement unit (IMU). The IMU may sense velocity andacceleration in the world frame, with respect to the gravity vector. Thevelocity and acceleration sensed by the IMU may then be translated tothat of the robotic system 100 based on the location of the IMU in therobotic system 100 and the kinematics of the robotic system 100.

The robotic system 100 may include other types of sensors not explicateddiscussed herein. Additionally or alternatively, the robotic system mayuse particular sensors for purposes not enumerated herein.

The robotic system 100 may also include one or more power source(s) 114configured to supply power to various components of the robotic system100. Among other possible power systems, the robotic system 100 mayinclude a hydraulic system, electrical system, batteries, and/or othertypes of power systems. As an example illustration, the robotic system100 may include one or more batteries configured to provide charge tocomponents of the robotic system 100. Some of the mechanical components110 and/or electrical components 116 may each connect to a differentpower source, may be powered by the same power source, or be powered bymultiple power sources.

Any type of power source may be used to power the robotic system 100,such as electrical power or a gasoline engine. Additionally oralternatively, the robotic system 100 may include a hydraulic systemconfigured to provide power to the mechanical components 110 using fluidpower. Components of the robotic system 100 may operate based onhydraulic fluid being transmitted throughout the hydraulic system tovarious hydraulic motors and hydraulic cylinders, for example. Thehydraulic system may transfer hydraulic power by way of pressurizedhydraulic fluid through tubes, flexible hoses, or other links betweencomponents of the robotic system 100. The power source(s) 114 may chargeusing various types of charging, such as wired connections to an outsidepower source, wireless charging, combustion, or other examples.

The electrical components 116 may include various mechanisms capable ofprocessing, transferring, and/or providing electrical charge or electricsignals. Among possible examples, the electrical components 116 mayinclude electrical wires, circuitry, and/or wireless communicationtransmitters and receivers to enable operations of the robotic system100. The electrical components 116 may interwork with the mechanicalcomponents 110 to enable the robotic system 100 to perform variousoperations. The electrical components 116 may be configured to providepower from the power source(s) 114 to the various mechanical components110, for example. Further, the robotic system 100 may include electricmotors. Other examples of electrical components 116 may exist as well.

Although not shown in FIG. 1, the robotic system 100 may include a body,which may connect to or house appendages and components of the roboticsystem. As such, the structure of the body may vary within examples andmay further depend on particular operations that a given robot may havebeen designed to perform. For example, a robot developed to carry heavyloads may have a wide body that enables placement of the load.Similarly, a robot designed to reach high speeds may have a narrow,small body that does not have substantial weight. Further, the bodyand/or the other components may be developed using various types ofmaterials, such as metals or plastics. Within other examples, a robotmay have a body with a different structure or made of various types ofmaterials.

The body and/or the other components may include or carry the sensor(s)112. These sensors may be positioned in various locations on the roboticdevice 100, such as on the body and/or on one or more of the appendages,among other examples.

On its body, the robotic device 100 may carry a load, such as a type ofcargo that is to be transported. The load may also represent externalbatteries or other types of power sources (e.g., solar panels) that therobotic device 100 may utilize. Carrying the load represents one exampleuse for which the robotic device 100 may be configured, but the roboticdevice 100 may be configured to perform other operations as well.

As noted above, the robotic system 100 may include various types oflegs, arms, wheels, and so on. In general, the robotic system 100 may beconfigured with zero or more legs. An implementation of the roboticsystem with zero legs may include wheels, treads, or some other form oflocomotion. An implementation of the robotic system with two legs may bereferred to as a biped, and an implementation with four legs may bereferred as a quadruped. Implementations with six or eight legs are alsopossible. For purposes of illustration, biped and quadrupedimplementations of the robotic system 100 are described below.

FIG. 2 illustrates a quadruped robot 200, according to an exampleimplementation. Among other possible features, the robot 200 may beconfigured to perform some of the operations described herein. The robot200 includes a control system, and legs 204A, 204B, 204C, 204D connectedto a body 208. Each leg may include a respective foot 206A, 206B, 206C,206D that may contact a surface (e.g., a ground surface). Further, therobot 200 is illustrated with sensor(s) 210, and may be capable ofcarrying a load on the body 208. Within other examples, the robot 200may include more or fewer components, and thus may include componentsnot shown in FIG. 2.

The robot 200 may be a physical representation of the robotic system 100shown in FIG. 1, or may be based on other configurations. Thus, therobot 200 may include one or more of mechanical components 110,sensor(s) 112, power source(s) 114, electrical components 116, and/orcontrol system 118, among other possible components or systems.

The configuration, position, and/or structure of the legs 204A-204D mayvary in example implementations. The legs 204A-204D enable the robot 200to move relative to its environment, and may be configured to operate inmultiple degrees of freedom to enable different techniques of travel. Inparticular, the legs 204A-204D may enable the robot 200 to travel atvarious speeds according to the mechanics set forth within differentgaits. The robot 200 may use one or more gaits to travel within anenvironment, which may involve selecting a gait based on speed, terrain,the need to maneuver, and/or energy efficiency.

Further, different types of robots may use different gaits due tovariations in design. Although some gaits may have specific names (e.g.,walk, trot, run, bound, gallop, etc.), the distinctions between gaitsmay overlap. The gaits may be classified based on footfall patterns—thelocations on a surface for the placement the feet 206A-206D. Similarly,gaits may also be classified based on ambulatory mechanics.

The body 208 of the robot 200 connects to the legs 204A-204D and mayhouse various components of the robot 200. For example, the body 208 mayinclude or carry sensor(s) 210. These sensors may be any of the sensorsdiscussed in the context of sensor(s) 112, such as a camera, LIDAR, oran infrared sensor. Further, the locations of sensor(s) 210 are notlimited to those illustrated in FIG. 2. Thus, sensor(s) 210 may bepositioned in various locations on the robot 200, such as on the body208 and/or on one or more of the legs 204A-204D, among other examples.

FIG. 3 illustrates a biped robot 300 according to another exampleimplementation. Similar to robot 200, the robot 300 may correspond tothe robotic system 100 shown in FIG. 1, and may be configured to performsome of the implementations described herein. Thus, like the robot 200,the robot 300 may include one or more of mechanical components 110,sensor(s) 112, power source(s) 114, electrical components 116, and/orcontrol system 118.

For example, the robot 300 may include legs 304 and 306 connected to abody 308. Each leg may consist of one or more members connected byjoints and configured to operate with various degrees of freedom withrespect to one another. Each leg may also include a respective foot 310and 312, which may contact a surface (e.g., the ground surface). Likethe robot 200, the legs 304 and 306 may enable the robot 300 to travelat various speeds according to the mechanics set forth within gaits. Therobot 300, however, may utilize different gaits from that of the robot200, due at least in part to the differences between biped and quadrupedcapabilities.

The robot 300 may also include arms 318 and 320. These arms mayfacilitate object manipulation, load carrying, and/or balancing for therobot 300. Like legs 304 and 306, each arm may consist of one or moremembers connected by joints and configured to operate with variousdegrees of freedom with respect to one another. Each arm may alsoinclude a respective hand 322 and 324. The robot 300 may use hands 322and 324 for gripping, turning, pulling, and/or pushing objects. Thehands 322 and 324 may include various types of appendages orattachments, such as fingers, grippers, welding tools, cutting tools,and so on.

The robot 300 may also include sensor(s) 314, corresponding to sensor(s)112, and configured to provide sensor data to its control system. Insome cases, the locations of these sensors may be chosen in order tosuggest an anthropomorphic structure of the robot 300. Thus, asillustrated in FIG. 3, the robot 300 may contain vision sensors (e.g.,cameras, infrared sensors, object sensors, range sensors, etc.) withinits head 316.

III. EXAMPLE ROBOT EMPLOYING DYNAMIC BALANCE FOR WHOLE BODY MANIPULATION

FIG. 4A illustrates an example biped robot 400 that includes a body 408defined by a lower body section 408 a, an upper body section 408 b, andan intermediate body section 408 c. The lower body section 408 a and theupper body section 408 b are coupled to the intermediate body section408 c. The lower body section 408 a includes two legs 404 and 406 thatgenerally extend downward to a surface (e.g., ground surface) from theintermediate body section 408 c. Like the legs 304 and 306 of the robot300, each leg 404, 406 may include one or more members connected byjoints and configured to operate with various degrees of freedom withrespect to one another. As shown in FIG. 4A, for instance, the leg 404includes at least members 404 a 1-a 2 and joints 404 b 1-b 2, and theleg 406 includes at least members 406 a 1-a 2 and joints 406 b 1-b 2.

Each leg 404, 406 may also include a respective foot 410, 412 toestablish direct contact with the surface. The legs 404, 406 can stablysupport the robot 400 on the surface. Additionally, the legs 404, 406enable the robot 400 to move at various speeds according to themechanics for different gaits. As shown in FIG. 4A, for instance, thelegs 404, 406 are operable to move the robot 400 according to at leastforward/backward translation along a y-axis and/or left/right lateraltranslation along a x-axis.

The upper body section 408 b includes end-effectors 422, 424 disposed onthe ends of respective arms 418, 420. The arms 418, 420 may extendoutwardly from the upper body section 408 b to position the respectiveend-effectors 422, 424. Like the arms 318, 320 of the robot 300, eacharm 418, 420 may include one or more members connected by joints andconfigured to operate with various degrees of freedom with respect toone another. As shown in FIG. 4A, for instance, the arm 418 includes atleast members 418 a 1-a 2 and joints 418 b 1-b 2, and the arm 420includes at least members 420 a 1-a 2 and joints 420 b 1-b 2.

The end-effectors 422, 424 may be employed to perform a task bymanipulating objects, acting on loads, etc. For instance, the robot 400may use the end-effector 422, 424 for gripping, turning, carrying,pulling, and/or pushing objects. As shown, the end-effectors 422, 424may be hand-like structures with movable fingers. Alternatively, theend-effectors 422, 424 may include other types of appendages orattachments, such as grippers, welding tools, cutting tools, and thelike.

As shown in FIG. 4A, the intermediate body section 408 c acts as, orresembles, a pelvis for the bipedal configuration of the robot 400. Theintermediate body section 408 c is supported by the lower body section408 a below, and correspondingly, the intermediate body section 408 csupports the upper body section 408 b above. As described further below,the intermediate body section 408 c may be positioned and/or oriented toallow for desired positioning and operation of the legs 404, 406 and theend-effectors 422, 424.

The robot 400 may include aspects of the robotic system 100 describedabove. In particular, sensors similar to the sensors 112 may provideinformation regarding the position and movement of a component of therobot 400 relative to other components and/or the external environment.As shown in FIG. 4A, for instance, the robot 400 may include sensors 414(e.g., cameras, infrared sensors, object sensors, range sensors, etc.)within a head 416.

Furthermore, as shown in FIG. 5, the robot 400 may include a controlsystem 417 with a lower body control system 417 a, an upper body controlsystem 417 b, and a master control system 417 c, each of which mayinclude aspects of the control system 118 described above. The lowerbody control system 417 a can operate aspects of the lower body section408 a. The upper body control system 417 b can operate aspects of theupper body section 408 b. The master controller 417 c can control otheraspects of the robot 400. The master controller 417 c may alsocoordinate the actions of the lower body control system 417 a and theupper body control system 417 b.

Each of the control systems 417 a-c may receive sensor data from thesensors to operate respective aspects of the robot 400. Although thecontrol systems 417 a-c are shown as separate elements in FIG. 5,aspects of the control systems 417 a-c may be implemented with commonhardware and/or software.

To achieve the desired positions for the feet 410, 412 and/or thedesired forces with the legs 404, 406, the lower body control system 417a may employ an inverse kinematics solver 419 a to determine thecorresponding positions of the joints and the orientations of themembers of the respective legs 404, 406. Meanwhile, to achieve desiredpositions for the end-effectors 422, 424, the upper body control system417 a may employ an inverse kinematics solver 419 b to determine thecorresponding positions of the joints and the orientations of themembers of the respective arms 418, 420.

In general, inverse kinematics refers to the use of the kinematicsequations of the robot 400 to determine the parameters for components,such as the joints of a leg 404, 406 or an arm 418, 420, to allow therespective foot 410, 412 or end-effector 422, 424 to reach a targetposition. A motion plan specifies the movement of the robot so that thefoot 410, 412 or the end-effector 422, 424 can reach a target position.The inverse kinematics solver 419 a, 419 b transforms the motion planinto actuator trajectories for components (e.g., the joints) of therobot 400.

The lower body control system 417 a can operate the legs 404, 406 tobalance the robot 400 dynamically on the surface, while the upper bodycontrol system 417 b operates the arms 418, 420 and the end-effectors422, 424 to perform a task. As shown in FIG. 4A, when the foot 410 is incontact with the surface, the leg 404 experiences a reaction forceF_(r1) in response to the force applied by the leg 404. Similarly, whenthe foot 412 is in contact with the surface, the leg 406 experiences areaction force F_(r2) in response to the force applied by the leg 406.Each reaction force F_(r1), F_(r2) may include components along one ormore of the x-, y-, and z-axes.

The lower body control system 417 a can dynamically control the legs404, 406 so that the reaction forces F_(r1), F_(r2) allow the robot 400to maintain a balance that supports the operation of the arms 418, 420and the end-effectors 422, 424. In response to any moments experiencedby the robot 400, the reaction forces F_(r1), F_(r2) may also produceopposing moments M_(r1), M_(r2), respectively, (not shown) to balancethe robot 400. The dynamic balancing provided by the legs 404, 406during operation of the end-effectors 422, 424 constitutes a whole bodymanipulation that more closely resembles actual motion by actual humans.

A. Example Balancing with the Lower Body

Referring to FIG. 4B, the robot 400 is supported on the surface solelyby the leg 404. The weight of the robot 400, i.e., a gravitational forceF_(gr), is applied via the foot 410 in the negative z-direction to thesurface. The gravitational force F_(gr) effectively acts at the centerof mass (COM) of the body 408 in the negative z-direction. A componentof the reaction force F_(r1) is applied in the positive z-direction atthe foot 410 with a magnitude equal to the gravitational force F_(gr).Thus, the gravitational force F_(gr) is balanced by the z-component ofthe reaction force F_(r1).

If, however, the center of mass of the robot 400 is not aligned with thefoot 410 along the x-axis and/or y-axis, the gravitational force F_(gr)may produce a moment M_(gr) at the foot 410. The moment M_(gr) mayinclude components about the x-axis and/or y-axis. The reaction forceF_(r1) includes a frictional force between the foot 410 and the surface,where the frictional force acts on the foot 410 in the x- and/ory-directions. The frictional force provides a torque that opposes themoment M_(gr) produced by the gravitational force F_(gr). If the momentM_(gr) does not exceed the maximum torque that can be provided by thefrictional force, the robot 400 can maintain a balance. On the otherhand, if the moment M_(gr) exceeds the maximum torque, the foot 410 mayslip and the moment M_(gr) may cause the robot 400 to lose balance.

With the foot 410 in a given position on the surface, the lower bodycontrol system 417 a can control the positions and orientations of themembers 404 a 1-a 2 and joints 404 b 1-b 2 to control the effect of thereaction forces F_(r1) on the leg 404 and to achieve a balance the body408. For instance, if the lower body control system 417 a determinesthat the robot 400 as shown in FIG. 4B cannot maintain balance due tothe moment M_(gr), the lower body control system 417 a can control themembers 404 a 1-a 2 and the joints 404 b 1-b 2 of the leg 404 toreposition the center of mass of the robot 400 into closer alignmentwith the foot 410 along the x-axis and/or y-axis. This can reduce themoment M_(gr) and allow the frictional force from the reaction forceF_(r1) to balance the robot 400 as described above.

As shown in FIG. 4B, when the lower body control system 417 arepositions the center of mass, the intermediate body section 408 c maycorrespondingly move in the x- and y-directions from a position (x_(i),y_(i), z_(i)) to a new position (x_(i)′. y_(i)′, z_(i)). Although thecenter of mass in FIG. 4B may appear to coincide with the intermediatebody section 408 c, it is understood that the center of mass may belocated at other positions relative to the robot 400.

Although not shown in FIG. 4B, the leg 406 may be manipulated in amanner similar to the leg 404. In general, with the feet 410, 412 ingiven positions on the surface, the lower body control system 417 a canreposition and/or reorient the members and joints of the legs 404, 406to control how the reaction forces F_(r1) and F_(r2) affect the body408. Specifically, the lower body control system 417 a can control thelegs so that the reaction forces F_(g1) and F_(g2) balance the body 408.

Indeed, both feet 410, 412 can simultaneously contact the surface andthe legs 404, 406 may experience reaction forces F_(r1) and F_(r2). Thegravitational force F_(gr) can be balanced by the sum of thez-components of the reaction forces F_(r1) and F_(r2). In addition, thelower body control system 417 a may control the members and joints ofboth legs 404, 406 to change the position of the center of mass andallow opposing moments M_(r1), M_(r2) from the reaction forces F_(r1),F_(r2) (e.g., frictional forces) to balance the moment M_(gr) from thegravitational force F_(gr).

B. Dynamic Balancing with the Lower Body to Support Operation ofEnd-Effectors

As described above, the upper body control system 417 b can operate eachend-effector 422, 424 to perform a respective task. To perform differenttasks, the upper body control system 417 b can move the end-effectors422, 424 with the arms 418, 420 to different positions in order to reachand move objects, act on loads, etc.

As shown in FIG. 4A, for instance, the end effector 424 is initiallypositioned at coordinates (x_(e2), y_(e2), z_(e2)). In FIG. 4C, theupper body control system 417 b repositions the end effector 424 to(x_(e2)′, y_(e2)′, z_(e2)′) to perform a task. To reposition, the upperbody control system 417 b operates the members 420 a 1-a 2 and joints420 b 1-b 2 of the arm 420 to extend the end-effector 424 to the targetposition (x_(e2)′, y_(e2)′, z_(e2)′).

Depending on the mass associated with the arms 418, 420, the position ofthe center of mass of the robot 400 may change when the arms 418, 420and corresponding end-effectors 422, 424 are repositioned. The change inthe position of the center of mass changes the effect of thegravitational force F_(gr) on the body 408. In particular, the momentM_(gr) produced by the gravitational force F_(gr) also changes. Tomaintain the balance of the robot 400, the members and joints of thelegs 404, 406 may need to be repositioned and/or reoriented to achievereaction forces F_(r1), F_(r2) that balance the new moment M_(g).

When performing a task, each end-effector 422, 424 may also experience arespective external end-effector force F_(e1), F_(e2), as shown in FIG.4A. For instance, if each end-effector 422, 424 is tasked with carryinga respective object, the respective end-effector force F_(e1), Fee mayinclude the weight of the respective object acting in the negativez-direction. In another instance, if the end-effectors 422, 424 aretasked with pushing a large object along the surface, the end-effectorforces F_(e1) and F_(e2) may include the opposing frictional forcesbetween the large object and the surface. Although both end-effectorforces F_(e1) and F_(e2) are shown in FIG. 4A, the end-effectors 410,412 do not necessarily experience the end-effector forces F_(e1) andF_(e2) simultaneously.

The robot 400 may thus experience the external forces F_(e1) and F_(e2)in addition to the gravitational force F_(gr). In addition, the robot400 may experience moments M_(e1), M_(e2) produced by the end-effectorforces F_(e1), F_(e2), respectively. As such, the lower body controlsystem 417 a can also account for the effects of the externalend-effector forces F_(e1) and F_(e2) as well as the gravitational forceF_(gr) to balance the robot 400 on the surface. In particular, the lowerbody control system 417 a can control the members and joints of the legs404, 406 to allow the reaction forces F_(r1), F_(r2) to balance the sumof the forces F_(e1), F_(e2), F_(gr) as well as the sum of momentsproduced by forces F_(e1), F_(e2), F_(gr).

For instance, if each end-effector 422, 424 is carrying an object, theend-effector forces F_(e1), F_(e2) include the weight of each objectacting in the negative z-direction. In addition to the gravitationalforce F_(gr), the legs 404, 406 apply the weight of each object to thesurface via the feet 410, 412. The reaction forces F_(r1), F_(r2)correspondingly apply a force in the positive z-direction to balance theforces applied by the legs 404, 406.

Moreover, in addition to the moment M_(gr) produced by the gravitationalforce F_(gr), the forces F_(e1), F_(e2) also produce moments M_(e1),M_(e2). The reaction forces F_(r1), F_(r2) correspondingly producemoments M_(r1), M_(r2) that oppose the moments M_(e1), M_(e2). The lowerbody control system 417 a can operate the members and joints of the legs404, 406 so that moments M_(r1), M_(r2) can balance the moments M_(e1),M_(e2). For instance, the reaction forces F_(r1), F_(r2) may includefrictional forces that act in the positive y-direction and provide atorque to oppose the moments M_(e1), M_(e2).

To allow the lower body control system 417 a to account for the forcesand moments produced by the positioning and manipulation of theend-effectors 422, 424, the upper control system 417 b may communicateinformation to the lower body control system 417 a relating to theposition of the end-effectors 422, 424 as well as the end-effectorforces F_(e1), F_(e2) and moments M_(e1), M_(e2). The upper body controlsystem 417 b, for instance, may receive signals from force and torquesensors to determine the end-effector forces F_(e1), F_(e2) and momentsM_(e1), M_(e2).

The upper body control system 417 b may control the end-effectors 422,424 to perform any number and sequence of tasks. As such, the arms 418,420 and the end-effectors 422, 424 may be in constant motion and mayexperience varying end-effector forces F_(e1), F_(e2). Advantageously,the lower body control system 417 a can dynamically balance the body 408to support the actions of the upper body section 408 b. The lower bodycontrol system 417 a can simultaneously operate the legs 404, 406 asdescribed above to provide continuous balance for continuous activity bythe upper body section 408 b. The upper body control system 417 b doesnot rely on the lower body control system 417 a to establish a staticbalance before operating the end-effectors 422, 424 to perform eachtask.

Because the lower body control system 417 a controls the lower bodysection 408 a, the upper body control system 417 b can control the upperbody section 408 b by representing and processing the lower body section408 a as a virtual link connected via the intermediate body section 408c. With the virtual link, the implementation of the control system 417is simplified because control of the lower body section 408 a and theupper body 408 b are divided between the lower body control system 417 aand the upper body control system 417 b, respectively. The upper bodycontrol system 417 b can generally assume that the lower body controlsystem 417 a will dynamically provide the balance to support the upperbody section 408 b as the upper body control system 417 b can focus onperforming tasks with the end-effectors 422, 424.

In addition to operating the arms 418, 420, the upper body controlsystem 417 b can position and/or orient the intermediate body section408 c relative to the lower body section 408 b to position and operatethe end-effectors 422, 424. The intermediate body section 408 c can bepositioned and/or oriented according to any one or more of the sixdegrees of freedom: (1) forward/backward translation along the y-axis;(2) left/right lateral translation along the x-axis; (3) up/downtranslation along the z-axis; (4) pitch rotation about the x-axis; (5)roll rotation about the y-axis; and (6) yaw rotation about the z-axis.For instance, to reach an object to the left of the robot 400, the upperbody control system 417 b may cause the intermediate body section 408 cto rotate about the z-axis (i.e., yaw rotation).

As described in an example above, the lower body control system 417 amay reposition the center of mass of the robot 400 along the x-axisand/or the y-axis to balance the body 408. This may also involvemovement by the intermediate body section 408 c along the x-axis(left/right lateral translation) and/or the y-axis (forward/backwardtranslation). Thus, to balance the body 408 with the lower body section408 a, the lower body control system 417 a may need to control one ormore degrees of freedom of the intermediate body section 408 c.

As a result, the upper body control system 417 b may be constrained frommoving the intermediate body section 408 c according to degrees offreedom that may affect the ability of the lower body section 408 a tobalance dynamically. The constraints free the lower body control system417 a to balance dynamically. Such constraints allow the upper bodycontrol system 117 b to represent or consider the lower body section 408a as the virtual link connected via the intermediate body section 408 c.

For instance, if the lower body control system 417 a needs to controlthe position of the intermediate body section 408 c along the x-axis(left/right lateral translation) and/or the y-axis (forward/backwardtranslation), the upper body control system 417 b may be constrainedfrom those degrees of freedom. The inverse kinematics solver 419 b forthe upper body control system 417 b may treat these two degrees offreedom as constraints when determining the positioning of theend-effectors 422, 424. As a result, the upper body control system 417 bcontrols the position of the intermediate body section 408 c accordingto any of the remaining four degrees of freedom, i.e., up/downtranslation along the z-axis, pitch rotation about the x-axis, rollrotation about the y-axis, and yaw rotation about the z-axis.

The end-effector forces F_(e1), F_(e2) generate a resulting linear forceF_(i) and/or moment M_(i) on the intermediate body section 408 c. FIG.4D illustrates an exploded view of the robot 400 with the linear forceF_(i) and moment M_(i) applied to the intermediate body section 408 c.Using force and torque sensors, for instance, the upper body controlsystem 417 b can determine the linear force F_(i) and moment M_(i) andcommunicate this information to the lower body control system 417 a. Assuch, the lower body control system 417 a can operate the legs 404, 406so that the reaction forces F_(r1), F_(r2) can balance the linear forceF_(i) and/or moment M_(i) at the intermediate body section 408 c.

As shown in FIG. 5, the upper body control system 417 b communicates thelinear force F_(i) and the moment M_(i) to the lower body control system417 a. In addition, the lower body control system 417 a controls theintermediate body section 408 c according a set DoF_(A) of one or moredegrees of freedom. Meanwhile, the upper body control system 417 bcontrols the intermediate body section 408 c according a different setDoF_(B) of one or more degrees of freedom which do not include those ofDoF_(A).

Furthermore, the lower body control system 417 a can dynamically balancethe linear force F_(i) and/or the moment M_(i) as they change with theoperation of the upper body section 408 b. The upper body control system417 b enables this dynamic balancing by communicating the changes to thelinear force F_(i) and the moment M_(i).

Accordingly, FIG. 6 illustrates an example process 500 for manipulatingthe lower body section 408 a to support activities performed by theupper body 408 b. In step 502, the upper body control system 417 boperates at least one of the end-effectors 422, 424. The at least oneend-effector 422, 424 experiences an end-effector force F_(e1), F_(e2)based on the operation by the upper body control system 417 b. Theintermediate body section 408 c experiences at least one of a firstintermediate body linear force F_(i) or a first intermediate body momentM_(i) based on the end-effector force F_(e1), F_(e2). In step 504, theupper body control system 417 b communicates, to the lower body controlsystem, information relating to the first intermediate body linear forceLand the first intermediate body moment M_(i).

In step 506, the lower body control system 417 a operates one or morelegs 404, 406 in response to the operation of at least one movableend-effector 422, 424. The one or more legs 404, 406 experiencerespective reaction forces F_(r1), F_(r2) from the surface based on theoperation by the lower body control system 417 a. The intermediate bodysection 408 c experiences at least one of a second intermediate bodylinear force or a second intermediate body moment based on the reactionforces F_(r1), F_(r2). Operation of the one or more legs 404, 406 by thelower body control system 417 a determines the second intermediate bodylinear force and/or the second intermediate body moment. The secondintermediate body linear force counteracts the first intermediate linearforce F_(i) the intermediate body section 408 c resulting from theend-effector forces F_(e1), F_(e2). The second intermediate body momentcounteracts the first intermediate body moment M_(i) on the intermediatebody section 408 c resulting from the end-effector forces F_(e1),F_(e2).

The process 500 may also include step 506 a where the lower body controlsystem 417 a positions the intermediate body section 408 c according toa first set of degrees of freedom based on the operation of the one ormore legs 404, 406. Correspondingly, the process 500 may additionallyinclude step 502 a where the the upper body control system 417 bpositions the intermediate body section 408 c in response to theoperation of the at least one movable end-effector 422, 424. Thispositioning of the intermediate body section 408 c by the upper bodycontrol system 417 b involves movement according to a second set ofdegrees of freedom. The upper body control system 417 b is constrainedfrom positioning the intermediate body section according to the firstset of degrees of freedom.

Although the upper body control system 417 b may communicate directlywith the lower body control system 417 a, the master controller 417 cmay also help coordinate the interaction between the lower body controlsystem 417 a and the upper body control system 417 b. For instance, theupper body control system 417 b may plan to move one of theend-effectors 422, 424 to a desired position. The master controller 417c can determine whether balance can be maintained by the currentposition of the feet 410, 412 if the upper body control system 417 battempts to move the end-effector 422, 424 to the desired position. Ifbalance cannot be maintained, the master controller 417 c can signal thelower body control system 417 a to move the feet 410, 412 to newpositions that allow the end-effector 422, 424 to be positioned morestably at the target positions. Alternatively, the lower body controlsystem 417 a may determine whether the robot 400 should be moved to thenew position.

In addition to controlling the members and joints of the legs 404, 406to achieve balance with the feet 410, 412 in given positions, the lowerbody control system 417 a may also reposition the feet 410, 412 on thesurface to change the reaction forces F_(r1) and F_(r2). Repositioningthe feet 410, 412 can also change the moments that the gravitationalforce F_(gr) produces at the feet 410, 412. The resulting reactionforces F_(r1) and F_(r2) may produce more effective balance for therobot 400.

As described above, the upper body control system 417 b can control theupper body section 408 b by representing and processing the lower bodysection 408 a as a virtual link connected via the intermediate bodysection 408 c. Advantageously, the virtual link allows positioning andmovement (velocity) of the end-effectors 422, 424 to be compensated formotions of the lower body section 408 a (also known as station keeping).For instance, if the upper body control system 417 b commands anend-effector 422, 424 to move at some velocity relative to somestationary object in the world, such movement should account for motionsof the lower body section 408 a even though the the upper body controlsystem 417 b does not have direct control of the lower body section 408a (which is primarily dealing with balance and locomotion). In thiscase, the lower body control system 417 a can estimate the virtual linkvelocity and pass the velocity to the upper body control system 417 b,which can then adjust the the inverse kinematics solver 419 baccordingly. The inverse kinematics solver 419 b may use the velocity ofthe virtual link to determine a motion plan for the upper body section408 b that achieves desired velocities for the end-effectors 422, 424 ina static world frame.

Although the examples described herein may achieve dynamic balancing inresponse to end-effector forces that are detected by force/torquesensors, dynamic balancing may also be achieved in other implementationsbased on calculations of expected or desired end-effector forces. Insuch implementations, the lower body control system 417 a advantageouslycompensates for the expected or desired end-effector forces preemptivelybefore any balance or positioning errors occur.

Furthermore, although the examples described herein may achieve dynamicbalancing in response to loads supported by the end-effectors, dynamicbalancing can also be achieved in other implementations when other loadsare additionally or alternatively experienced by the upper body section.For instance, upper body section may experience dynamic forces, such asforces required to accelerate an arm, an end-effector, or a payload,during high-speed motions. Such dynamic forces also generate a resultinglinear force and/or moment on the intermediate body section, which thelower body control can also balance with the reaction forces.

C. Balancing the Lower Body to Support Operation of End-Effectors DuringMovement by the Robot

The lower body control system 417 a can additionally control thereaction forces F_(r1) and F_(r2) to move the robot 400 according to adesired gait. For instance, rather than solely controlling the leg 404to balance the robot 400 as shown in FIG. 4B, the lower body controlsystem 417 a can also operate the leg 406 to plant the foot 412 on thesurface. The resulting reaction force F_(r2) can produce an opposingmoment M_(r2) to balance the moment M_(gr) produced by the gravitationalforce F_(gr). As such, planting the foot 412 on the surface to balancethe moment M_(gr) may constitute a step in a gait.

Once the foot 412 is planted and the robot 400 is balanced, the lowerbody control system 417 a can operate the legs 404, 406 to repositionthe center of mass and produce another moment M_(gr) with thegravitational force F_(gr). The moment M_(gr) causes the body 408 tofall forward, but the lower body control system 417 a can operate theleg 404 to swing the foot 410 forward and plant the foot 410 on thesurface. The resulting reaction force F_(r1) on the foot 410 producesanother opposing moment M_(r1) that balances the moment M_(gr). As such,planting the foot 410 on the surface constitutes a second step.Alternately repeating the steps by the feet 410, 412 results in a gait.As described, the lower body control system 417 a can establish a stateof balance with each alternating step, before causing the body 408 tofall forward again for the next step.

The reaction forces F_(r1) and F_(r2) are not limited to balancing theeffect of the gravitational force F_(gr). When each foot 410, 412contacts the surface, the lower body control system 417 a may operatethe respective leg 404, 406 to apply additional forces to the surface.For instance, the legs 410, 412 may apply forces in the negativey-direction. In response to this force, a y-component of the respectivereaction force F_(r1), F_(r2) acts on the feet 410, 412 in the positivey-direction. This y-component results from the friction between the feet410, 412 and the surface. Accordingly, the ground reaction forcesF_(r1), F_(r2) apply forces which can help push the body 408 forward inthe positive-y direction. Thus, the application of forces in thenegative y-direction may constitute pushes off the surface to achieve afaster gait.

Additionally or alternatively, the legs 410, 412 may apply forces to thesurface in the positive or negative x-direction. In response to thisforce, a x-component of the respective ground reaction force F_(r1),F_(r2) acts on the feet 410, 412 in the opposing x-direction. Thisx-component results from the friction between the feet 410, 412 and thesurface. Accordingly, the reaction forces F_(r1), F_(r2) apply forceswhich can help push the body 408 laterally in the positive and/ornegative x-direction.

The lower body control system 417 a can dynamically balance the body 408to allow the end-effectors 422, 424 to be positioned and operated whilethe robot 400 is moving according to a gait. Indeed, the robot 400 canwalk or run along a ground surface, and due to the dynamic balancing,the robot 400 can simultaneously operate the arm 418 to position theend-effector 422, e.g., to grab an object, without interrupting thegait. To produce a balance for desired operation of the end-effectors422, 422 at a given time during the gait, the lower body control system417 a can account for the additional forces applied/experienced by thelegs 404, 406 as the robot 400 moves according to the gait. To achievethe desired reaction forces F_(r1), F_(r2) for balancing and moving thebody 408, the lower body control system 417 a may employ inversekinematics to determine corresponding velocities for positioning andorienting the members and joints of the legs 404, 406. Furthermore, thelower body control system 417 a can dynamically adjust thepositioning/repositioning of the feet 410, 412 to maintain the gaitduring the balancing process described above.

IV. CONCLUSION

In view of the foregoing, a robot can operate its legs to dynamicallybalance itself on a surface while operating its end-effectors. When thelegs contact a surface (e.g., ground surface), the legs apply forces tothe surface and experience reaction forces from the surface. The robotcan dynamically control the legs so that the reaction forces allow therobot to maintain a balance that supports the operation of theend-effectors.

Although example implementations may include a biped robot, otherconfigurations may include a lower body that provides dynamic balancingwhile an upper body performs tasks with one or more end-effectors. Inaddition, although the examples above may describe balancing the forcesF_(e1), Fee and moments M_(e1), M_(e2) associated with the end-effectors422, 424, it is understood that a robot may experience forces andmoments from loads at other components of the robot. For instance, robotmay include a receptacle for carrying cargo. The robot can achievedynamic balancing by similarly accounting for these other loads.

The above detailed description describes various features and functionsof the disclosed systems, devices, and methods with reference to theaccompanying figures. In the figures, similar symbols typically identifysimilar components, unless context indicates otherwise. The illustrativeimplementations described in the detailed description, figures, andclaims are not meant to be limiting. Other implementations can beutilized, and other changes can be made, without departing from thescope of the subject matter presented herein. It will be readilyunderstood that the aspects of the present disclosure, as generallydescribed herein, and illustrated in the figures, can be arranged,substituted, combined, separated, and designed in a wide variety ofdifferent configurations, all of which are explicitly contemplatedherein.

With respect to any or all of the message flow diagrams, scenarios, andflow charts in the figures and as discussed herein, each step, blockand/or communication may represent a processing of information and/or atransmission of information in accordance with example implementations.Alternative implementations are included within the scope of theseexample implementations. In these alternative implementations, forexample, functions described as steps, blocks, transmissions,communications, requests, responses, and/or messages may be executed outof order from that shown or discussed, including in substantiallyconcurrent or in reverse order, depending on the functionality involved.Further, more or fewer steps, blocks and/or functions may be used withany of the message flow diagrams, scenarios, and flow charts discussedherein, and these message flow diagrams, scenarios, and flow charts maybe combined with one another, in part or in whole.

A step or block that represents a processing of information maycorrespond to circuitry that can be configured to perform the specificlogical functions of a herein-described method or technique.Alternatively or additionally, a step or block that represents aprocessing of information may correspond to a module, a segment, or aportion of program code (including related data). The program code mayinclude one or more instructions executable by a processor forimplementing specific logical functions or actions in the method ortechnique. The program code and/or related data may be stored on anytype of computer-readable medium, such as a storage device, including adisk drive, a hard drive, or other storage media.

A computer-readable medium may include non-transitory computer-readablemedia such as computer-readable media that stores data for short periodsof time like register memory, processor cache, and/or random accessmemory (RAM). The computer-readable media may also includenon-transitory computer-readable media that stores program code and/ordata for longer periods of time, such as secondary or persistent longterm storage, like read only memory (ROM), optical or magnetic disks,and/or compact-disc read only memory (CD-ROM), for example. Thecomputer-readable media may also be any other volatile or non-volatilestorage systems. A computer-readable medium may be considered acomputer-readable storage medium, for example, or a tangible storagedevice.

Moreover, a step or block that represents one or more informationtransmissions may correspond to information transmissions betweensoftware and/or hardware modules in the same physical device. However,other information transmissions may be between software modules and/orhardware modules in different physical devices.

While various aspects and implementations have been disclosed herein,other aspects and implementations will be apparent to those skilled inthe art. The various aspects and implementations disclosed herein arefor purposes of illustration and are not intended to be limiting, withthe true scope being indicated by the following claims.

What is claimed is:
 1. A robot system comprising: a body comprising: anupper body section comprising a movable end-effector; a lower bodysection comprising a leg configured to contact a surface; and anintermediate body section coupling the upper body section and the lowerbody section; and a control system implemented with a processor, thecontrol system comprising: an upper body control system configured tooperate the movable end-effector, the movable end-effector experiencingan end-effector force based on the operation by the upper body controlsystem, and the intermediate body section experiencing at least one of afirst intermediate body linear force or a first intermediate body momentbased on the end-effector force; and a lower body control systemconfigured to: receive, from the upper body control system, informationrelating to the first intermediate body linear force and the firstintermediate body moment; and operate the leg in response to theoperation of the movable end-effector, the leg experiencing a respectivereaction force from the surface based on the operation by the lower bodycontrol system, and the intermediate body section experiencing at leastone of a second intermediate body linear force or a second intermediatebody moment based on the respective reaction force, wherein the lowerbody control system is configured to operate the leg so that the secondintermediate body linear force balances the first intermediate bodylinear force and the second intermediate body moment balances the firstintermediate body moment.
 2. The robot system of claim 1, wherein theupper body control system is configured to process the lower bodysection as a virtual link coupled to the intermediate body section. 3.The robot system of claim 1, wherein: the lower body control system isfurther configured to position the intermediate body section using afirst set of degrees of freedom based on the operation of the leg; theupper body control system is further configured to position theintermediate body section using a second set of degrees of freedom basedon the operation of the movable end-effector; and the upper body controlsystem is constrained from positioning the intermediate body sectionusing the first set of degrees of freedom.
 4. The robot system accordingto claim 3, wherein: positioning the intermediate body section using thefirst set of degrees of freedom translates the intermediate body sectionalong a first axis and a second axis; and positioning the intermediatebody section using the second set of degrees of freedom rotates theintermediate body section about three axes and translates theintermediate body section along a third axis.
 5. The robot systemaccording to claim 1, wherein: the lower body section comprises twolegs, and each leg includes a respective foot configured to contact thesurface directly; for a given position of each foot, the lower bodycontrol system is configured to determine whether the secondintermediate body linear force can balance the first body intermediatelinear force and the second intermediate body moment can balance thefirst intermediate body moment; and in response to determining that thesecond intermediate body linear force cannot balance the firstintermediate body linear force or the second intermediate body momentcannot balance the first intermediate body moment, the lower bodycontrol system is configured to reposition at least one of the feet onthe surface.
 6. The robot system according to claim 5, wherein the lowerbody control system is configured to adjust the repositioning of the atleast one of the feet according to a gait.
 7. The robot system of claim1, wherein the lower body control system is configured to operate theleg in response to the operation of the movable end-effector while theleg is moving according to a gait.
 8. A robot system comprising: a bodycomprising: an upper body section comprising a movable end-effector; alower body section comprising a leg configured to contact a surface; andan intermediate body section coupling the upper body section and thelower body section; and a control system implemented with a processor,the control system comprising: an upper body control system configuredto operate the upper body section, the intermediate body sectionexperiencing at least one of a first intermediate body linear force or afirst intermediate body moment based on the operation of the upper bodysection; and a lower body control system configured to operate the lowerbody section in response to the operation of the upper body section, theintermediate body section experiencing at least one of a secondintermediate body linear force or a second intermediate body momentbased on reaction forces from operation of the lower body section,wherein the lower body control system is configured to operate the lowerbody section so that the second intermediate body linear force balancesthe first intermediate body linear force and the second intermediatebody moment balances the first intermediate body moment, and wherein theupper body control system is constrained from using a same set ofdegrees of freedom to position the intermediate body section that thelower body control system uses to position the intermediate bodysection.
 9. The robot system of claim 8, wherein the upper body controlsystem is configured to communicate, to the lower body control system,information relating to the first intermediate body linear force and thefirst intermediate body moment.
 10. The robot system of claim 8, whereinthe upper body control system is configured to process the lower bodysection as a virtual link coupled to the intermediate body section. 11.The robot system according to claim 8, wherein: the lower body controlsystem is configured to position the intermediate body section using afirst set of degrees of freedom to translate the intermediate bodysection along a first axis and a second axis; and the upper body controlsystem is configured to position the intermediate body section using asecond set of degrees of freedom to rotate the intermediate body sectionabout three axes and translate the intermediate body section along athird axis.
 12. The robot system according to claim 8, wherein: thelower body section comprises two legs, and each leg includes arespective foot configured to contact the surface directly; for a givenposition of each foot, the lower body control system is configured todetermine whether the second intermediate body linear force can balancethe first intermediate body linear force and the second intermediatebody moment can balance the first intermediate body moment; and inresponse to determining that the second intermediate body linear forcecannot balance the first intermediate body linear force or the secondintermediate body moment cannot balance the first intermediate bodymoment, the lower body control system is configured to reposition atleast one of the feet on the surface.
 13. The robot system according toclaim 12, wherein the lower body control system is configured to adjustthe repositioning of the at least one of the feet according to a gait.14. The robot system of claim 8, wherein the lower body control systemis configured to operate the lower body section in response to theoperation of the movable end-effector while the leg is moving accordingto a gait.
 15. A method for controlling a robot system, the methodcomprising: operating, by an upper body control system of the robotsystem, a moveable end-effector of an upper body section of the robotsystem to cause the moveable end-effector to experience an end-effectorforce and an intermediate body section of the robot system to experienceat least one of a first intermediate body linear force or a firstintermediate body moment based on the end-effector force, theintermediate body section coupling the upper body section to a lowerbody section of the robot system, the lower body section comprising aleg configured to contact a surface; communicating, from the upper bodycontrol system to a lower body control system of the robot system,information relating to the first intermediate body linear force and thefirst intermediate body moment; and in response to operating themoveable end-effector, operating, by the lower body control system, theleg to cause the leg to experience a respective reaction force from thesurface and the intermediate body section to experience at least one ofa second intermediate body linear force or a second intermediate bodymoment based on the respective reaction force, the operation of the legbalances the second intermediate body linear force and the firstintermediate body linear force and balances the second intermediate bodymoment and the first intermediate body moment.
 16. The method of claim15, further comprising abstracting, by the upper body control system,the lower body section as a virtual link coupled to the intermediatebody section.
 17. The method of claim 15, further comprising:positioning, by the lower body control system, the intermediate bodysection using a first set of degrees of freedom based on the operationof the leg; and positioning, by the upper body control system, theintermediate body section using a second set of degrees of freedom basedon the operation of the moveable end-effector, the upper body controlsystem constrained from using the first set of degrees of freedom toposition the intermediate body section.
 18. The method of claim 17,wherein: positioning the intermediate body section using the first setof degrees of freedom translates the intermediate body section along afirst axis and a second axis; and positioning the intermediate bodysection using the second set of degrees of freedom rotates theintermediate body section about three axes and translates theintermediate body section along a third axis.
 19. The method of claim15, wherein the lower body section comprises two legs and each legincludes a corresponding foot configured to contact the surfacedirectly, and the method further comprises: for a given position of eachfoot, determining, by the lower body control system, whether the secondintermediate body linear force can balance the first intermediate bodylinear force and the second intermediate body moment can balance thefirst intermediate body moment; and in response to determining that thesecond intermediate body linear force cannot balance the firstintermediate body linear force or the second intermediate body momentcannot balance the first intermediate body moment, repositioning, by thelower body control system, at least one of the feet on the surface. 20.The method of claim 19, further comprising adjusting, by the lower bodycontrol system, the repositioning of the at least one of the feet on thesurface according to a gait.
 21. The method of claim 15, furthercomprising moving the leg according to a gait, wherein operating the legin response to the operation of the moveable end-effector occurs duringthe gait.
 22. A method for controlling a robot system, the methodcomprising: operating, by an upper body control system of the robotsystem, an upper body section of the robot system to cause anintermediate body section of the robot system to experience at least oneof a first intermediate body linear force or a first intermediate bodymoment based on the operation of the upper body section, the upper bodysection comprising a movable end-effector and the intermediate bodysection coupling the upper body section to a lower body section of therobot system, the lower body section comprising a leg configured tocontact a surface; in response to operating the upper body section,operating, by a lower body control system of the robot system, the lowerbody section to cause the leg to experience a respective reaction forcefrom the surface and the intermediate body section to experience atleast one of a second intermediate body linear force or a secondintermediate body moment based on the respective reaction force, theoperation of the lower body section balancing the second intermediatebody linear force and the first intermediate body linear force andbalancing the second intermediate body moment and the first intermediatebody moment; positioning, by the upper body control system, theintermediate body section using a first set of degrees of freedom,wherein the lower body control system is constrained from using thefirst set of degrees of freedom to position the intermediate bodysection.
 23. The method of claim 22, further comprising abstracting,with the upper body control system, the lower body section as a virtuallink coupled to the intermediate body section.
 24. The method of claim22, further comprising positioning, by the lower body control system,the intermediate body section using second set of degrees of freedombased on the operation of the lower body section.
 25. The method ofclaim 24, wherein: positioning the intermediate body section using thesecond set of degrees of freedom translates the intermediate bodysection along a first axis and a second axis; and positioning theintermediate body section using the first set of degrees of freedomrotates the intermediate body section about three axes and translatesthe intermediate body section along a third axis.
 26. The method ofclaim 22, wherein the lower body section comprises two legs and each legincludes a corresponding foot configured to contact the surfacedirectly, and the method further comprises: for a given position of eachfoot, determining, by the lower body control system, whether the secondintermediate body linear force can balance the first intermediate bodylinear force and the second intermediate body moment can balance thefirst intermediate body moment; and in response to determining that thesecond intermediate body linear force cannot balance the firstintermediate body linear force or the second intermediate body momentcannot balance the first intermediate body moment, repositioning, by thelower body control system, at least one of the feet on the surface. 27.The method of claim 26, further comprising adjusting, by the lower bodycontrol system, the repositioning of the at least one of the feet on thesurface according to a gait.
 28. The method of claim 22, furthercomprising moving the leg according to a gait, wherein operating thelower body section in response to the operation of the upper bodysection occurs during the gait.